Variable modulation unicast system

ABSTRACT

A system is described that consists of a variable modulation unicast system that utilizes multiple modulation schemes in a cable network for unicast applications and is capable of assigning users to different channels of differing modulation schemes in the network based on a feedback signal received in response to a transmitted probe signal. The system may also, in response to the feedback signal from a remote device in the network, assign a channel from a plurality of channels having differing carrier frequencies and modulation schemes to the remote device and may also modify the carrier frequencies of the channels.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of and claims benefit to U.S.Non-Provisional Application No. 10/925,365 filed Aug 23, 2004, U.S. Pat.No. 7,937,738 issued May 3, 2011.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to broadband communication networks and inparticular to broadband communication networks utilizing coaxial cable.

2. Related Art

The worldwide utilization of external television (“TV”) antennas forreceiving broadcast TV signals, and of cable TV and satellite TV isgrowing at a rapid pace. These television signals from an external TVantenna, cable TV and satellite TV (such as from direct broadcastsatellite “DBS” systems) are usually received externally to a building(such as a home or an office) at a point-of-entry (“POE”). There may bemultiple TV receivers and/or video monitors within the building andthese multiple TV receivers may be in signal communication with the POEvia a broadband cable network that may include a plurality of broadbandcables and broadband cable splitters. Generally, these broadband cablesplitters distribute downstream signals from the POE to variousterminals (also known as “nodes”) in the building. The nodes may beconnected to various types of customer premise equipment (“CPE”) such ascable converter boxes, televisions, video monitors, cable modems, cablephones and video game consoles.

Typically, these broadband cable networks are implemented utilizingcoaxial cables and coaxial cable splitters, respectively. Additionally,in the case of cable TV or satellite TV, the multiple TV receivers maybe in signal communication with the broadband cable network via aplurality of cable converter boxes, also known as set-top boxes(“STBs”), that are connected between the multiple TV receivers and thebroadband cable network via a plurality of network nodes.

Typically, a STB connects to a coaxial cable from a network node (suchas the wall outlet terminal) to receive cable TV and/or satellite TVsignals. Usually, the STB receives the cable TV and/or satellite TVsignals from the network node and converts them into tuned TV signalsthat may be received by the TV receiver and/or video signals that may bereceived by a video monitor.

In FIG. 1, an example known broadband cable network 100 (also known as a“cable system” and/or “cable wiring”) is shown within a building 102(also known as customer premises or “CP”) such as a typical home oroffice. The broadband cable network 100 may be in signal communicationwith an optional cable service provider 104, optional broadcast TVstation 106, and/or optional DBS satellite 108, via signal path 110;signal path 112, external antenna 114 and signal path 115; and signalpath 116, DBS antenna 118 and signal path 119; respectively. Thebroadband cable network 100 also may be in signal communication withoptional CPEs 120, 122 and 124, via signal paths 126, 128 and 130,respectively.

In FIG. 2, another example known broadband cable network is shown withina building (not shown) such as a typical home. The cable network 200 maybe in signal communication with a cable provider (not shown), and/orsatellite TV dish (not shown), and/or external antenna (not shown) via asignal path 202 such as a main coaxial cable from the building to acable connection switch (not shown) outside of the building. The cablenetwork 200 may include a POE 204 and main splitter 206, a sub-splitter208, and STBs A 210, B 212 and C 214.

Within the cable network 200, the POE 204 may be in signal communicationwith main splitter 206 via signal path 216. The POE 204 may be theconnection point from the cable provider, which is, located external tothe building of the cable network 200. The POE 204 may be implemented asa coaxial cable connector, transformer and/or filter.

The main splitter 206 may be in signal communication with sub-splitter208 and STB A 210 via signal paths 218 and 220, respectively. Thesub-splitter 208 may be in signal communication with STB B 212 and STB C214 via signal paths 222 and 224, respectively. The main splitter 206and sub-splitter 208 may be implemented as coaxial cable splitters. TheSTBs A 210, B 212 and C 214 may be implemented by numerous well-knownSTB coaxial units such as cable television set-top boxes and/orsatellite television set-top boxes. Typically, the signal paths 202,216, 218, 220, 222 and 224 may be implemented utilizing coaxial cables.

In an example operation, the cable network 200 would receive CATV,and/or broadcast TV and/or satellite TV signals 226 via signal path 202at the POE 204. The POE 204 may pass, transform and/or filter thereceived RF signals to a second RF signal 228 that may be passed to themain splitter 206 via signal path 216. The main splitter 206 may thensplit the second RF signal 228 into split RF signals 230 and 232. Thesplit RF signal 230 is then passed to the sub-splitter 208 and the splitRF signal 232 is passed to the STB A 210 via signal paths 218 and 220,respectively. Once the split RF signal 232 is received by the STB A 210,the STB A 210 may convert the received split RF signal 232 into abaseband or RF signal 238 that may be passed to a video monitor or a TVset (not shown) in signal communication with the STB A 210.

Once the split RF signal 230 is received by the sub-splitter 208, thesub-splitter 208 splits the received split RF signal 230 into sub-splitRF signal 234 and 236 that are passed to STB B 212 and STB C 214 viasignal paths 222 and 224, respectively. Once the sub-split RF signals234 and 236 are received by the STB B 212 and STB C 214, the STB B 212and STB C 214 may convert the received sub-split RF signals 234 and 236into baseband or RF signals 240 and 242, respectively, that may bepassed to video monitors or TV sets (not shown) in signal communicationwith STB B 212 and STB C 214, respectively.

Unfortunately, the cable network 200 may introduce significant lossesfrom the POE 204 to STB A 210, STB B 212 and STB C 214 based on thequality of the splitters and coaxial cables. These losses may result indegraded signal levels at STB A 210, STB B 212 and STB C 214. In thepast, while utilizing analog transmission schemes, these degraded signallevels usually resulted in some loss in reception quality at STBs asevidenced by such anomalies as ghost and noisy images on some attachedvideo monitors or TV sets.

Unfortunately, these problems have become more important as many cabletelevision providers transition from analog to digital transmissions.Unlike analog transmissions, digital transmissions do not graduallydegrade with the transmission channel path performance. Typically,digital transmissions operate in an all or nothing fashion because ifthe performance of the transmission channel supports the digitaltransmission, the digital transmission is transmitted through thechannel with sufficient quality that results in no visual degradation.Alternatively, if the performance of the transmission channel does notsupport the digital transmission, the digital transmission will transmitthrough the channel in a degraded fashion that may result in no videooutput at the corresponding STB.

Generally, the United States Federal Communication Commission (“FCC”)recommends that analog channels be transmitted at 0 dBmV power level atthe TV set in order to produce high quality video signals. However, mostcable providers currently transmit digital transmissions at lower powerlevels because digital transmissions are more robust.

Presently, many cable providers that transmit digital cable signalsutilize quadrature amplification modulation (“QAM”) modulation schemes.Multi-level QAM modulation schemes are well known to those skilled inthe art. Typically most cable providers that transmit digital cablesignals utilize 64 QAM and 256 QAM modulation schemes and many cableproviders are considering transmitting digital cable signals at 1024QAM.

Unfortunately, digital modulation schemes only operate over channelsthat have good enough transmission performance capable of supporting thegiven digital modulation scheme. The higher the digital modulationscheme the higher the needed performance of the channel.

The coaxial cable distribution to a building is controlled by the cablecompany and typically conforms to well-defined criteria. The in-homecable distribution is typically provided by the homebuilder and is notwell controlled, thus possibly resulting in a wide variation inreception. In a typical building 102 the performance of the coaxialcable depends on the coaxial cable distribution 110 and the performanceof the building cable wiring in the broadband cable network 100. Themeasurement of the total signal performance is represented by the outputpower received at each node (not shown) connecting the broadband cablenetwork 100 at the different CPEs (such as CPEs 120, 122 and 124).Typically, the output power at each node experiences a large amount ofpower variance from node to node that may be a result of the splittersand cables within the broadband cable network 100.

If the output power level at any node is below the needed power level tosupport the digital modulation scheme transmitted by the cable provider,the cable provider will have to remediate to ensure adequateperformance. Usually, the output power level is measured as a signalmetric such as the signal-to-noise ratio (“SNR” or “S/N”) of thereceived signal at the CPE attached at the node, or the received powerlevel P.

As an example, in most cable set-top boxes (“STB”) used as a CPE, a 64QAM modulation scheme typically requires about 23 to 24 dBmV SNR tooperate. Similarly, 256 QAM requires about 30 to 32 dBmV and 1024 QAMrequires about 36 to 38 dBmV.

If the SNR is not high enough to support the transmitted digital signalthen the cable provider must remediate by means that include eitheramplifying the transmitted signal at the POE 204 or elsewhere, runningnew cable from the POE 204 to the node having the problem, ortransmitting a lower order digital modulation scheme. Unfortunately,infrastructure remediation is difficult, time consuming, labor intensiveand expensive.

As a result, many cable providers find it difficult to transmit higherthan 64 or 256 QAM signals even though much of the cable plant might beable to support higher constellations. Unfortunately, the lowermodulation scheme results in cable providers utilizing the cablebandwidth less efficiently. This results in a lower number of optionsfor special unicast services such as cable modem applications and videoon demand (“VoD”) services.

With the advent of cable modems and VoD, more and more end users aredemanding these services. Cable providers, however, only have limitedbandwidth to with which to operate.

Therefore, there is a need for a system and method to reduce thebandwidth limitations of the existing cable network for unicastapplications such as cable modem and VoD transmission. Additionally,there is a need for a system and method to vary the digital modulationscheme for transmitting to each CPE in a cable network in order tooptimize the cable provider's bandwidth.

SUMMARY

A system is described that consists of a variable modulation unicastsystem that utilizes multiple modulation schemes in a cable network forunicast applications and is capable of assigning users to differentchannels of differing modulation schemes in the network. As an exampleof operation, the variable modulation unicast system transmits a firstsignal to at least one remote device of a plurality of remote devices,receives a feedback signal from the at least one remote device inresponse to the transmitted probe signal, and determines the modulationscheme in response to the feedback signal. The variable modulationunicast system may also, in response to the feedback signal, assign achannel from a plurality of channels having differing carrierfrequencies and modulation schemes, to a remote device in the network.As another example of operation, the variable modulation unicast systemmay also receive a feedback signal from at least one remote device of aplurality of remote devices that includes a direct request or a directcommand for a specific modulation scheme, and then assign a channelhaving that modulation scheme to that at least one remote device. Thevariable modulation unicast system is also capable of modifying thecarrier frequencies of the channels.

Other systems, methods, features and advantages of the invention will beor will become apparent to one with skill in the art upon examination ofthe following figures and detailed description. It is intended that allsuch additional systems, methods, features and advantages be includedwithin this description, be within the scope of the invention, and beprotected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingfigures. The components in the figures are not necessarily to scale,emphasis instead being placed upon illustrating the principles of theinvention. In the figures, like reference numerals designatecorresponding parts throughout the different views.

FIG. 1 is a block diagram of an example of an implementation of a knownbroadband cable network within a building.

FIG. 2 is a block diagram of another example of an implementation of aknown broadband cable network within the building shown in FIG. 1.

FIG. 3 is a block diagram of an example of an implementation of avariable modulation unicast system within a cable network in accordancewith the present invention.

FIG. 4 is a block diagram of an example of an implementation of thevariable modulation unicast system shown in FIG. 3.

FIG. 5 is a graph of an example of a plot of the power level versus nodeoutput for each receiving node in a cable network similar to the oneshown in FIG. 3.

FIG. 6 is a graph of an example of a plot of the modulation scheme typeversus node output for each receiving node in the cable network shown inFIG. 3 corresponding to the power levels shown in the plot of FIG. 4.

FIG. 7 is a flowchart illustrating an example of a method performed bythe variable modulation unicast system shown in FIG. 3.

FIG. 8 is a flowchart illustrating another example of a method performedby the variable modulation unicast system.

DETAILED DESCRIPTION

In the following description of the preferred embodiment, reference ismade to the accompanying drawings that form a part hereof, and in whichis shown by way of illustration a specific embodiment in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

FIG. 3 is a block diagram of an example of an implementation of avariable modulation unicast system (“VMUS”) 300 within a cable network302 in accordance with the present invention. The cable network 302 mayalso include a cable provider 304 and a plurality of customer premises(“CPs”) 306, 308 and 310 where each CP 306, 308 and 310 may be abuilding such as a multi-dwelling unit or a home. It is appreciated thatwhile only three CPs 306, 308 and 310 are shown, the cable network 302may include any number of CPs. Each CP may be in signal communicationwith the VMUS 300 via signal paths 312, 314 and 316, respectively.Additionally, the cable provider 304 also may be in signal communicationwith the Internet 318 and the telephone system and cable TV programmingsources 319.

As an example, CP 306 may be a home with two remote devices receivingcable television programming from the cable provider 304. Examples ofthe two remote devices may be two customer premises equipment (“CPEs”)322 and 324. In this example, CP 306 may include a point-of-entry(“POE”) 326, a broadband cable network 328 and the two CPEs 322 and 324.The CPEs 308 and 310 may include, for example, set-top converter boxes(“STBs”) for converting the received cable signals into video signals,cable-ready televisions, cable telephones, video monitors, video gameconsoles, cable-ready components and appliances and cable modems.

Again, it is appreciated that while only two remote devices (CPEs 322and 324) are shown, the CP 306 may include any number of remote devices.As an example, many people today have numerous televisions sets in theirhomes and many also have cable modems for connecting to the Internet 318as well as cable telephones for connecting to the telephone system 320via the cable network 302. Additionally, numerous CPs (including CPs 308and 310) may also have numerous remote devices that may be similar toCPE 322 and CPE 324.

The POE 326 may be any connection, coupler, switch, filter and/or relaythat is capable of connecting the signal path 312 from the cableprovider 304 to the broadband cable network 328. The broadband cablenetwork 328 may include a plurality of broadband cables (not shown) andbroadband cable splitters (not shown). These broadband cables andbroadband cable splitters may be implemented utilizing coaxial cablesand coaxial cable splitters, respectively. Additionally, the broadbandcable splitters may distribute downstream signals from the POE 326 tovarious terminals (also known as “nodes”) in the building. The nodes(not shown) are connected to CPEs 322 and 324. Also, the broadband cablenetwork 328, in addition to coaxial cables and splitters, may includeadditional passive and active devices such as bi-directional and/oruni-directional amplifiers, filters, diplexers and other RF componentsand subsystems.

As an example of operation, the VMUS 300 may be utilized to reduce thebandwidth limitations of the cable network 302 for unicast applicationssuch as cable modem and video-on-demand (“VoD”) transmission to theremote devices (such as CPE 322 and CPE 324) on the cable network 302.In general, the VMUS 300 reduces the bandwidth limitation of the cablenetwork 302 by varying the digital modulation schemes utilized fortransmitting to each remote device in the cable network 302 in order tooptimize the bandwidth of the cable network 302.

In operation, the VMUS 300 may transmit a first signal to at least oneremote device from a plurality of remote devices, where the first signalutilizes a first modulation scheme. The VMUS 300 may then receive afeedback signal from the remote device, where the feedback signal mayinclude identification information for the remote device and a firstmetric value representative of the transmission characteristics of achannel-path to the remote device. In response to the received feedbacksignal, the VMUS 300 may determine a second modulation scheme that itmay utilize to transmit a second signal to the remote device. The VMUS300 may also assign a home-channel, having a home-channel frequency, tothe remote device in response to the received first metric value andidentification information for the remote device. The VMUS 300 may thentransmit the second signal to the remote device utilizing thehome-channel.

An example of an architecture for the VMUS 300 may include a transmitter(not shown) capable of transmitting a first signal to at least oneremote device, where the first signal utilizes a first modulationscheme. The VMUS 300 may also include a receiver (not shown) capable ofreceiving a feedback signal from the remote device in response to thetransmitted first signal, where the feedback signal includesidentification information for the remote device and a first metricvalue representative of the transmission characteristics of achannel-path to the remote device. The VMUS 300 may further include acontroller (not shown) capable of determining a second modulation schemein response to the received first metric signal and instructing thetransmitter to transmit a second signal to the remote device, where thesecond signal utilizes the second modulation scheme.

In FIG. 4, a block diagram of the VMUS 300 is shown in signalcommunication with the CP 400 via signal path 402. The VMUS 300 islocated at a premises of the cable provider 304 and may be in signalcommunication with information content 404 provided by the cableprovider 304 to the CP 400. As an example of an implementation of thearchitecture, the VMUS 300 may include a variable modulation module 406,transmitter 408, diplexer 410, receiver 412, controller 414 and storageunit 416 having a database 418. The variable modulation module 406 maybe in signal communication with the information content 404 andtransmitter 408 via signal paths 420 and 422, respectively. The diplexer410 may be in signal communication with transmitter 408 and receiver 412via signal paths 424 and 426, respectively. The controller 414 may be insignal communication with the variable modulation module 406, receiver412 and storage unit 416 via signal paths 428, 430 and 432,respectively.

The CP 400 may include POE 434, broadband cable network 436 and remotedevices CPE 438, CPE 440 and CPE 442. The CPE 438 may include a metricmeasurement unit A 444, CPE 440 metric measurement unit B 446, and CPE442 metric measurement unit C 448. The broadband cable network 436 is insignal communication with POE 434, CPE 438, CPE 440 and CPE 442 viasignal paths 450, 452, 454 and 456, respectively. Again, it isappreciated that while only three CPEs 438, 440 and 442 are shown, CP400 may include any number of CPEs. The CPEs 438, 440 and 442 mayinclude, for example, STBs, cable-ready televisions, cable telephones,video monitors, video game consoles, cable-ready components andappliances and cable modems.

The POE 434 may be any connection, coupler, switch, filter and/or relaythat is capable of connecting the signal path 402 from the cableprovider 304 to the broadband cable network 436. The broadband cablenetwork 436 may include a plurality of broadband cables (not shown),broadband cable splitters (not shown), and unidirectional orbidirectional amplifiers (not shown) or other devices. These broadbandcables and broadband cable splitters may be implemented utilizingcoaxial cables and coaxial cable splitters, respectively. Additionally,the broadband cable splitters may distribute downstream signals from thePOE 434 to CPEs 438, 440 and 442 through the signal paths 452, 454 and456, respectively, and may distribute upstream signals from CPEs 438,440 and 442 through the signal paths 452, 454, and 456, respectively.

The variable modulation module 406 is capable of transmitting QAM (i.e.,Quadrature Amplitude Modulation) signals over multiple channels atdifferent modulations and of switching the modulation scheme utilized byeach channel in modulating the information content 404 based on theinstructions from the controller 414 via signal path 428. The VMUS 300,utilizing instructions from the controller 414 via signal path 428 tothe variable modulation module 406, is also capable of switching contentfrom one modulated channel at one frequency to another modulated channel(with similar or different modulation and/or modulation scheme) at adifferent frequency. Examples of variable modulation module 406 includethe Motorola® SmartStream Encryptor Modulator (SEM) and theScientific-Atlanta® Model D9476 16/64/128/256 Modulator (for broadcast).

The transmitter 408 may be a standard cable-type headend transmitterthat is well known to those skilled in the art. The transmitter 408 iscapable of transmitting the modulated signal 458 produced by thevariable modulator module 406 to CP 400. An example of transmitter 408is the Motorola® Commander 8 (CM8) upconverter.

The receiver 412 may be the standard cable type upstream receiver at thecable provider 304 capable of receiving control signals from the remotedevices (such as CPEs 438, 440 and 442), and can be a DOCSIS or anout-of-band (OOB) receiver utilized for receiving cable modem returnchannel or STB return channel information. Examples of receiver 412include the Motorola® Omnistar® Dual Return Path Receiver and theScientific-Atlanta® Atlas Mk II—Digital Terrestrial Receiver. Thereceiver 412 may receive control signals from the remote devices andpass the control information 460 to the controller 414 via signal path430. The diplexer 410 may be any standard diplexer capable of allowingthe transmitter 408 to transmit signals to CP 400, via signal paths 424and 402, while also allowing the receiver 412 to receive control signalsfrom CP 400 via signal paths 402 and 426. The transmitter 408 and thereceiver may comprise a single unit (for example, theScientific-Atlanta® Prisma GbE™ OpticalTransmitter/Receiver/Transceiver). Also, the variable modulation module406 and the transmitter 408 may comprise a single unit (for example, theScientific-Atlanta® Continuum DVP™ Dense QAM Array [for Voice-on-Demanddelivery]).

The controller 414 may be any processor, microprocessor, and/ormicrocontroller type of device capable of controlling the modulationscheme produced by the variable modulation module 406. Examples of thecontroller 414 include the Motorola® NC 1500 Network Controller and theScientific-Atlanta® C-100 Multiplexer Controller. The controller 414 maybe in signal communication with the storage unit 416 for storing datarelating to the feedback signals received from the remote devices. Thestorage unit 416 may include a memory unit such as a flash non-volatilememory, read-access memory (“RAM”) or any other type of memory storagedevice. The storage unit 416 may also include a database 418 storedwithin the memory unit for storing the control-related information fromthe remote devices.

The metric measurement unit A 444, metric measurement unit B 446 andmetric measurement unit C 448 may be any measurement device capable ofmeasuring signal metric values at the remote devices CPE 438, 440 and442, respectively. Examples of the metric values may include thesignal-to-noise ratio (also known as the “SNR” and “S/N”), the bit-errorrate (“BER”), the packet error rate (“PER”), and the power level and anyother similar measurement of the received signal at the correspondingremote device. However, other signal-performance metric values are alsopossible without departing from the scope of the invention.

The metric values measured by the metric measurement unit A 444, metricmeasurement unit B 446 and metric measurement unit C 448 or arepresentative metric value derived from a plurality of such metricvalues, may be selectively transmitted to the VMUS 300 by way of thefeedback signal in order to determine the signal performance of thereceived signals from the VMUS 300 at the remote devices. As analternative to a metric value or a representative metric value, thefeedback signal may include a direct request or a direct command fromthe corresponding CPE (438, 440 or 442) to the controller 414 to sendfuture information to the CPE (438, 440 or 442) at a given modulationscheme, such as 64, 256 or 1024 QAM. In this case, the CPE itselfutilizes the metric information to compute a corresponding modulationscheme and informs the controller 414 about the desired modulationtogether with the identity of the sending CPE. The controller 414receives the information through the receiver 412, verifies that anappropriate carrier with the appropriate modulation scheme is available,informs the CPE (438, 440, 442) about the transition and then sends allfuture unicast information to the CPE (438, 440, 442) over the newmodulation scheme.

In operation, the VMUS 300 transmits a first signal to the plurality ofremote devices that include CPE 438, CPE 440, CPE 442 and others. Thefirst signal may be modulated utilizing a first modulation schemeproduced by the variable modulation module 406 and transmitted on onechannel. The VMUS 300 may transmit the first signal utilizing aknown-channel where the known-channel has a known-channel carrierfrequency. The known-channel may then function as a “log-on-channel”that allows the remote devices to tune to and receive the known-channeland access (i.e., “log-on” to) the cable provider 304.

As an example of a remote device, CPE 438 may receive the transmittedfirst signal and in response determine the metric value of the receivedfirst signal with metric measurement unit A 444. The metric value may bea measure of the transmission characteristics of the channel-path fromthe VMUS 300 to CPE 438 where the channel-path would include thetransmission path through the transmission line (such as a coaxialcable) along signal path 402, POE 434, the transmission line alongsignal path 450, broadband cable network 436 and the transmission linealong signal path 452. If the characteristics of the transmission linealong signal path 402 are known, the metric value may also be a measureof the transmission characteristics of the channel-path from the POE 434to the CPE 438.

In this example, the representative metric value may be derived frommeasured values that may include the measured SNR and/or the BER and/orthe PER and/or the power level of the received first signal at CPE 438.CPE 438 may then produce a feedback signal that includes therepresentative metric value and some type of identification informationfor CPE 438. In the case of CPE 438 being a cable modem, theidentification information may also include the Internet Protocol (“IP”)address for the CPE 438. CPE 438 then transmits the feedback signal tothe VMUS 300 through signal path 452, broadband cable network 436,signal path 450, POE 434 and signal path 402. In the case of CPE 438being a cable modem, the feedback signal may be transmitted to the VMUS300 utilizing a control-channel defined by Data Over Cable ServiceInterface Specifications (“DOCSIS”). The CPE can also send back theinformation over the out-of-band (OOB) return channel, which iscurrently being utilized by cable STBs to send information back for VODand other control functions.

The VMUS 300 receives the feedback signal with receiver 412 and producesthe control information signal 460 that includes the representativemetric value and identification information from the received feedbacksignal. The control information signal 460 is passed to the controller414 and the controller 414 in response may determine a second modulationscheme that is better suited for unicast type transmissions to CPE 438.The controller 414 may utilize a threshold detector (not shown) todetermine the second modulation scheme. If the controller 414 determinesthat another modulation scheme should be utilized in unicasttransmissions to CPE 438, the controller 414 instructs the variablemodulation module 406 to switch to another modulation scheme on a secondchannel when transmitting unicast services to CPE 406. The VMUS may alsodetermine that the carrier frequency of a channel should be changed toaccommodate the requirements of the system; that is, if another channelis required for the second modulation scheme, the controller 414 mayinstruct the variable modulation module 406 to assign a differentcarrier frequency to a channel, and then that channel would be used totransmit unicast services to CPE 406.

The controller 414 then stores in storage unit 416 (via signal path 432)the identification information, the representative metric value and theselected modulation scheme for CPE 438. The VMUS 300 then transmits asecond signal to CPE 438 where the second signal utilizes a secondmodulation scheme. The second modulation scheme corresponds to theselected modulation scheme from the controller 414 and the second signalmay be transmitted utilizing a new home-channel that has a home-channelcarrier frequency different than the known-channel carrier frequency. Inthis example, CPE 438 would then potentially be able to tune to the newhome-channel and receive unicast services at a different modulationscheme. Once CPE 438 tunes to the new home-channel, CPE 438 may againmeasure the transmission characteristics of the home-channel and sendback a new feedback signal with metric values associated with the newhome-channel. This allows the VMUS to again change the selectedmodulation scheme in response to a change in the transmissioncharacteristics of the new home-channel.

As an example, if CPE 438 is capable of receiving signals from the VMUS300 at 1024 QAM and CPE 440 is capable of receiving signals at 256 QAMbut some other remote devices on the cable network 302 are only capableof receiving signals from the VMUS 300 at 64 QAM, the cable provider 304typically will only transmit broadcast signals (i.e., signalstransmitted to all remote devices) at 64 QAM to ensure that all remotedevices receive the broadcast signals. However, the VMUS 300 allowstransmission on a unicast basis to both CPE 438 and CPE 440 atmodulation schemes higher than 64 QAM. These unicast transmissions mayinclude unicast services associated with either cable modem DOCSISservices or VoD. In this example, the VMUS 300 would transmit unicastservices to CPE 438 at 1024 QAM while at the same time transmittingunicast services to CPE 440 at 256 QAM and 64 QAM to other remotedevices.

The VMUS 300 may receive a plurality of feedback signals from theplurality of remote devices and store the received metric values orrepresentative metric values, as the case may be, and identificationinformation for each remote device in the storage unit 416. This storedinformation may be organized in a database 418 and this database 418 maybe utilized by the VMUS 300 to adaptively adjust the unicast channeldistribution of transmitted channels to the remote devices as needed.

FIG. 5 is a graph of an example of a plot 500 of the measured powerlevel 502 in dBmV versus node number 504 for each receiving node (notshown) connected to a remote device in several cable networks similar tothe one shown in 302. This graph is a summary of real cable systemmeasurements. Typically, if the remote device is a digital STB, thenoise figure of the remote device is approximately 8 dBmV, which resultsin approximately −49.6 dBmV noise floor for a 6 MHz cable channel. It isappreciated by those skilled in the art, that the −49.6 dBmV iscalculated by taking the thermal noise in combination with the noisefigure of 8 dBmV and a channel bandwidth of 6 MHz and a typical roomtemperature using a standard calculation. Also, for simplicity, thenoise floor power level may be rounded to −50 dBmV without affecting thebasics of the presented analysis.

As a result, in order to calculate the approximate SNR at a remotedevice the power received at the remote device is subtracted by −50dBmV. As an example, if the power received at the remote device is −20dBmV the resulting SNR would be 30 dBmV by subtracting the noise floorpower from the signal power.

In order to receive 64 QAM at a remote device, the remote devicetypically needs the received signals to have about 23 to 24 dBmV of SNR.In order to receive 256 QAM, the received signals should have about 29to 30 dBmV of SNR, and 36 to 38 dBmV of SNR is typically needed for 1024QAM.

In FIG. 6 a graph of an example of a plot 600 of the modulation schemetype (QAM) 602 versus node number 604 for each remote device connectedto a receiving node in the cable network 302 is shown. The modulationscheme type 602 values for each node number correspond to the powerlevels 502 shown in the plot 500, FIG. 5.

The modulation scheme types are shown as having three threshold valuesat 1024 QAM 604, 256 QAM 606 and 64 QAM 608. The 1024 QAM threshold 604corresponds to signals having at least −12 dBmV of measured power levelat the remote device, the 256 QAM threshold 606 corresponds to signalshaving at least −20 dBmV of measured power level at the remote device,and the 64 QAM threshold 606 corresponds to signals having between −20dBmV and −26 dBmV of measured power level at the remote device. Thecontroller 414, FIG. 4, or each of the CPEs (438, 440, 442) may utilizethese threshold values to determine proper modulation schemes totransmit to particular remote device.

FIG. 7 is a flowchart 700 illustrating an example of a method performedby the VMUS 300. The process starts in step 702 and in step 704, theVMUS 300 transmits a first signal to the plurality of remote devices. Instep 706, a remote device receives the first signal through achannel-path of transmission and, in step 708, the remote devicedetermines the transmission characteristics of the channel-path bymeasuring the characteristics of the received first signal at the remotedevice. In step 710, the remote device produces a feedback signal inresponse to determining the transmission characteristics of thechannel-path where the feedback signal includes a metric value andidentification information for the remote device. The remote device thentransmits the feedback signal to the VMUS 300, in step 712, and the VMUSreceives the feedback signal in step 714. The controller 414 thenreceives the metric value from the feedback signal and determines themodulation scheme to utilize with the remote device for unicasttransmissions.

As an example, if the VMUS 300 operates utilizing the three modulationschemes of 1024 QAM, 256 QAM and 64 QAM, the controller 414 may utilizea threshold detector to determine the proper modulation scheme to usebased on the value of the received metric value from the remote device.Assuming in this example that the remote device needs the receivedsignals at the remote device to have about 36 to 38 dBmV of SNR in orderto receive 1024 QAM, the controller 414 may utilize a first thresholdhaving a value of approximately 40 dBmV. Similarly, if the remote deviceneeds the received signals at the remote device to have about 30 dBmV ofSNR in order to receive 256 QAM, the controller 414 may utilize a firstthreshold having a value of approximately 32 dBmV. If the receivedsignals have less than 32 dBmV the VMUS 300 may default to transmittingat 64 QAM.

As a result, in decision step 716, if the received metric value isgreater than or equal to the first threshold (such as 40 dBmV of SNR),the process continues to step 718 where the VMUS 300 sets the modulationscheme to 1024 QAM and the process continues to step 720. If instead, indecision step 716, the received metric value is less than the firstthreshold, the process continues instead to decision step 722.

In decision step 722, if the metric value is greater than or equal to asecond threshold (such as 32 dBmV), the process continues to step 724where the VMUS 300 sets the modulation scheme to 256 QAM and the processcontinues to step 720. If instead, in decision step 722, the receivedmetric value is less than the second threshold, the process continuesinstead to step 726 where the VMUS 300 sets the modulation scheme to 64QAM and the process again continues to step 720.

In step 720, the VMUS 300 stores the identification information, metricvalue and modulation scheme in a storage unit 416 and, in step 728, theVMUS 300 receives a plurality of feedback signals from the plurality ofremote devices in response to the transmitted first signal. The VMUS 300then stores the plurality of identification information, metric valuesand modulation schemes for each remote device in the storage unit 730and, in step 732, the VMUS 300 organizes the stored data for each remotedevice in a database. Finally, the VMUS 300 adaptively adjusts theunicast channel distribution of the transmitted channels to the remotedevices as needed based on the database in step 734. The process ends instep 736. Also, the threshold values in 716 and 816 and also in 722 and822 can have different values at different times. For example, theprocess may start with an initial threshold for each of the modulationschemes, such as 40 dBmV for 1024 QAM and 32 dBmV for 256 QAM. Once aCPE modulation has been adjusted, a decision on a new threshold may bemade in such a way as to prevent frequent switching from occurring. Forexample, if the original threshold for using 1024 QAM requires SNRgreater than 40 dBmV, then switching back to 256 QAM may not occur untilthe SNR drops below 38 dBmV. This prevents a frequent switching back andforth if the real SNR is just around 40 dBmV and fluctuates slightly dueto differences in measurements or very small differences in channelconditions. This concept also applies for all other thresholds in FIG.7. and FIG. 8.

FIG. 8 is a flowchart 800 illustrating another example of a methodperformed by the VMUS 300. The process starts in step 802 and in step804, the VMUS 300 broadcasts a first signal to the plurality of remotedevices. In step 806, a plurality of remote devices receives the firstsignal through their respective channel-paths of transmission and, instep 808, each remote device determines the transmission characteristicsof their respective channel-paths by measuring the characteristics ofthe received first signal at the remote device. In step 810, each remotedevice produces a feedback signal in response to determining thetransmission characteristics of their respective channel-paths where thefeedback signal includes a metric value and identification informationfor the remote device. The remote devices then transmit the feedbacksignals to the VMUS 300, in step 812, and the VMUS receives the feedbacksignal in step 814. As in FIG. 7, the controller 414 then receives themetric value from the feedback signal and determines the modulationscheme to utilize with a particular remote device for unicasttransmissions.

Using the same example as in FIG. 7, if the VMUS 300 operates utilizingthe three modulation schemes of 1024 QAM, 256 QAM and 64 QAM, thecontroller 414 may utilize a threshold detector to determine the propermodulation scheme to use based on the value of the received metric valuefrom the remote device. Assuming again that the remote device needs thereceived signals at the remote device to have about 38 dBmV of SNR inorder to receive 1024 QAM, the controller 414 may utilize a firstthreshold having a value of approximately 40 dBmV. Similarly, if theremote device needs the received signals at the remote device to haveabout 30 dBmV of SNR in order to receive 256 QAM, the controller 414 mayutilize a first threshold having a value of approximately 32 dBmV. Ifthe received signals have less than 32 dBmV the VMUS 300 may default totransmitting at 64 QAM.

As a result, in decision step 816, if the received metric value isgreater than or equal to the first threshold (such as 40 dBmV of SNR),the process continues to decision step 818. If the received metric valueis less than the first threshold, the process continues to decision step822. In decision step 818, the VMUS 300 determines if a 1024 QAM channelis available, and if so, the process continues to step 820 where a 1024QAM channel is selected. If instead, in decision step 818, there is no1024 QAM channel available, the process continues instead to decisionstep 824.

In decision step 822, if the metric value is greater than or equal to asecond threshold (such as 32 dBmV of SNR), the process continues todecision step 824. If the received metric value is less than the firstthreshold, the process continues to step 828, where a 64 QAM channel isselected by default. In decision step 824, the VMUS 300 determines if a256 QAM channel is available, and if so, the process continues to step826 where a 256 QAM channel is selected. If instead, in decision step824 there is no 256 QAM channel available, the process continues to step828, where a 64 QAM channel is selected by default.

In step 830, the VMUS sends a message to the remote device thatidentifies the channel selected by the VMUS 330 in decision steps 818,826, or 828 for that channel. In step 832, the VMUS 300 stores theidentification information, metric value and channel selected in storageunit 416. In step 732, the VMUS 300 organizes the stored data for eachremote device and channel in a database. Finally, the VMUS 300, indecision step 836, determines if there is another feedback signal to beprocessed, and if so, the process repeats itself by going to decisionstep 816. Otherwise the process ends in step 840.

The processes in FIGS. 7 and 8 may be performed by hardware or software.If the process is performed by software, the software may reside insoftware memory located on the storage unit 416 or controller 414 in theVMUS 304. The software in software memory may include an ordered listingof executable instructions for implementing logical functions (i.e.,“logic” that may be implemented either in digital form such as digitalcircuitry or source code or in analog form such as analog circuitry oran analog source such an analog electrical, sound or video signal), mayselectively be embodied in any computer-readable (or signal-bearing)medium for use by or in connection with an instruction execution system,apparatus, or device, such as a computer-based system,processor-containing system, or other system that may selectively fetchthe instructions from the instruction execution system, apparatus, ordevice and execute the instructions.

In the context of this document, a “computer-readable medium” and/or“signal-bearing medium” is any means that may contain, store,communicate, propagate, or transport the program for use by or inconnection with the instruction execution system, apparatus, or device.The computer readable medium may selectively be, for example but notlimited to, an electronic, magnetic, optical, electromagnetic, infrared,or semiconductor system, apparatus, device, or propagation medium. Morespecific examples, i.e., “a non-exhaustive list” of thecomputer-readable media, would include the following: an electricalconnection (electronic) having one or more wires, a portable computerdiskette (magnetic), a RAM (electronic), a read-only memory “ROM”(electronic), an erasable programmable read-only memory (EPROM or Flashmemory) (electronic), an optical fiber (optical), and a portable compactdisc read-only memory “CDROM” (optical). Note that the computer-readablemedium may even be paper or another suitable medium upon which theprogram is printed, as the program can be electronically captured, viafor instance, optical scanning of the paper or other medium, thencompiled, interpreted or otherwise processed in a suitable manner ifnecessary, and then stored in a computer memory.

While various embodiments of the invention have been described, it willbe apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible that are within the scopeof this invention.

What is claimed is:
 1. A method for a selecting a channel from aplurality of channels for assignment to a remote device in a variablemodulation unicast system, the method comprising: transmitting aplurality of first signals to a plurality of remote devices over aplurality of channel-paths to the plurality of remote devices, whereineach first signal utilizes a first modulation scheme; receiving aplurality of feedback signals from the plurality of remote devices inresponse to transmitting the first signals, wherein each feedback signalincludes identification information for a corresponding remote device ofthe plurality of remote devices and a first metric value representativeof the transmission characteristics of the channel-path to thecorresponding remote device; assigning a first assigned-channel havingan assigned-channel carrier frequency from the plurality of channels tothe corresponding remote device in response to the received first metricsignal from the corresponding remote device, wherein assigning the firstassigned-channel to the corresponding remote device further includes:determining the availability of a subplurality of channels from theplurality of channels in response to the statistical information,wherein the availability of the channel is determined in response to thefirst metric values and identification information related to thecorresponding remote devices previously assigned to the subplurality ofchannels; determining a modular scheme compatible with each of thesubplurality of channels and the corresponding remote device; andselecting a channel from the subplurality of channels; and transmittinga second signal to the corresponding remote device, wherein the secondsignal includes information identifying the first assigned-channeldetermined in response to the received first metric signal.
 2. Themethod of claim 1, further including: storing the first metric value,identification information and first assigned-channel assigned to thecorresponding remote device in a storage unit; and determiningstatistical information from the first metric values, identificationinformation and first assigned-channels related to each of thecorresponding remote devices.
 3. The method of claim 2, wherein thestorage unit includes a memory unit.
 4. The method of claim 3, whereinthe storage unit includes a database.
 5. The method of claim 1, furtherincluding modifying the carrier frequency of the first assigned-channelin response to the statistical information determined from the firstmetric values, identification information and assigned-channels relatedto the corresponding remote devices.
 6. The method of claim 1, whereinthe first metric value is determined at the corresponding remote devicein response to determining the transmission characteristics of thechannel-path at the corresponding remote device.
 7. The method of claim6, wherein the first metric value representative of the transmissioncharacteristics of the channel-path at the corresponding remote deviceis determined by the corresponding remote device.
 8. The method of claim1, wherein transmitting a first signal further includes transmitting thefirst signal over a known-channel utilizing a known-channel carrierfrequency.
 9. The method of claim 8, wherein the feedback signal isreceived on a control-channel utilizing a control-channel frequency. 10.The method of claim 9, wherein the first metric value represents theSNR, the BER, the PER, or the power level of the received first signalat the corresponding remote device.
 11. The method of claim 10, whereinthe corresponding remote device is a cable modem.
 12. The method ofclaim 11, wherein the cable modem utilizes a Data Over Cable ServiceInterface Specifications (“DOCSIS”) protocol.
 13. The method of claim11, wherein the control-channel utilizes the DOCSIS protocol.
 14. Themethod of claim 10, wherein the corresponding remote device is a Set-TopBox (“STB”) capable of receiving Video-on-Demand (“VOD”) signals. 15.The method of claim 14, wherein the control-channel utilizes the STBout-of-band (OOB) channel
 16. The method of claim 10, wherein the atleast one remote device is a Set-Top Box (“STB”) capable of receivingVOD signals.
 17. The method of claim 8, wherein the identificationinformation includes the Internet Protocol (“IP”) address associatedwith the corresponding remote device.
 18. The method of claim 17,wherein transmitting the second signal to the corresponding remotedevice utilizing the first assigned-channel further includestransmitting all VOD signals and all DOCSIS signals.